For an organic light-emitting device, light is emitted by an organic thin film formed of an organic light-emitting material. In conventional structures of a pixel unit, the luminance of the organic light-emitting device depends on the thickness of the organic thin film, and the entire organic light-emitting device has a uniform luminance when the organic thin film has a uniform thickness. In practice, however, the thickness of the organic thin film of the organic light-emitting device is not uniform due to the imperfection of the manufacture process.
For example, a solution process may be employed to form the organic thin film in the procedure of manufacturing the organic light-emitting device, which is applicable for a polymeric organic light-emitting material and a soluble-micromolecule organic light-emitting material and is characterized by the low cost for manufacture apparatus, thereby having a distinct advantage in massive production for large sizes. In the case of manufacturing a full-color organic light-emitting device, an inkjet printing technology, among the technologies of solution process, is generally used. In the inkjet printing technology, the solution is jetted into a pixel region accurately by a piezoelectric nozzle and then the solvent of the solution is removed by evaporation, such that the organic thin film is formed within the pixel region. However, due to the difference of the evaporation rate of the solvent at an edge area and at a central area of the pixel region, it is difficult to form an organic thin film having a uniform thickness within the pixel region.
FIG. 1 shows a structure of a pixel unit in the prior art, the pixel unit including a substrate 100, a pixel defining layer 101, a pair of pixel electrodes 102 and 104, and an organic-light-emitting-display-device functional layer (i.e., an organic thin film) 103. A pixel region is defined by the pixel defining layer 101, the pixel electrode 102 is positioned within the pixel region, and the organic-light-emitting-display-device functional layer 103 is positioned on the pixel electrode 102. After preparing the organic-light-emitting-display-device functional layer 103 by the inkjet printing technology and the like, since the solvent at the edge area of the organic-light-emitting-display-device functional layer 103 has a higher vapor pressure than that of the solvent at the central area of the organic-light-emitting-display-device functional layer 103, the evaporation rate of the solvent at the edge area is faster than that of the solvent at the central area, such that the concentration of the solution at the edge area of the organic-light-emitting-display-device functional layer 103 is higher than that of the solution at the central area thereof, and the solution at the central area may flow towards the edge area, which causes the thickness of the edge area of the organic-light-emitting-display-device functional layer 103 to be always greater than that of the central area. When a voltage is applied to the organic-light-emitting-display-device functional layer 103 by the pixel electrodes 102 and 104, both the edge area and the central area of the functional layer 103 may emit light, and the luminance of the central area of the pixel region is higher than that of the edge area of the pixel region due to the nonuniformity of the thickness of the functional layer 103, which causes the nonuniformity of the luminance of the organic light-emitting device.
In the prior art, the nonuniformity of the thickness of the organic thin film is decreased by using inkjet printing solutions which have different boiling points, adjusting the structure of the pixel defining layer, or performing surface treatment on the pixel defining layer. For example, in the European patent document EP1729358A1, the nonuniformity of the thickness of the organic thin film is decreased by the structure design of the pixel defining layer; and in the US patent publication document US 2011/0008590 A1, the shape and thickness of the organic thin film formed by the inkjet printing technology are controlled by using different high-boiling-point solutions. However, the nonuniformity of thickness of the organic thin film cannot be eliminated completely by the above technical solutions, and when using conventional structures of a pixel unit, the luminance of the central area of the pixel region in the light emitting device is higher than that of the edge area thereof due to the nonuniformity of thickness of the organic thin film.